We propose to use selected mutants and recombinant DNA's to study two objectives related to tRNA function: 1) Plasmids containing tRNA genes are being manipulated in vitro to produce new species of tRNA in vivo in order to study the effects of tRNA sequence on function. Some tRNA mutants are being used for the same purposes. 2) Plasmids containing a cloned tRNA gene which alters the performance of the stringent-relaxed control circuit will be used to study the control of stable RNA synthesis and the role of the nearly universal tRNA sequence GT psi G.